As digital technology evolves, household appliances such as digital refrigerators, digital air conditioners and digital washing machines, and a variety of electronic devices including digital television receivers, digital video/audio devices and the like are emerging. Various home network technologies have been proposed to facilitate control of such electronic devices. E.g., a user may connect the electronic devices with an interface cable and control the operation of other devices by using a television receiver or a computer system having a display screen as a control device. Examples of home networking technologies for connecting electronic devices include Living network Control Protocol (LnCP) based on PLC (Power Line Communication), Universal Plug and Play (UPnP) based on HTML (Hyper Text Markup Language), HNCP (Home Network Control Protocol), HAVi (Home Audio/Video interoperability), and RS-485 interface.
The RS-485 interface is an electrical interface defined by the EIA/TIA-485 interface. The physical connector and pin arrangement are not specified. It is defined as the lowest layer of field buses such as BITBUS, PROFIBUS and INTERBUS specified in IEEE 1118. The RS-485 interface is well-suited for distributed control and automation, is robust to noise, and supports a multi-drop communications environments. In addition, the RS-485 interface can communicate at the rate up to 12 Mbps, providing sufficient communications speed for home networking applications at home. In addition, the bus structure does not affect another device when it is added or removed.
In an RS-485 interface communications system, one of several electronic devices connected to an RS-485 interface may be designated as a master device, such that it controls overall data transmission/reception. The master device refers to a device controlling the overall transmission/reception in a network in which a number of devices are connected by the RS-485 interface, and the slave devices refer to all other devices except the master device.
In the RS-485 interface communications system, the master device and the slave devices communicate with each other by polling based on the identification numbers (IDs) of the counterpart devices.
FIG. 1 illustrates an example of a preexisting network 100 of electronic devices connected through an RS-485 interface. Referring to FIG. 1, a communication is started when master device 101 sends a request packet for polling to slave devices 102 through 105 via a transmission line. The request packet sent by the master device 101 includes the identification number of the slave device to receive the request packet. Each of the slave devices 102 through 105 connected to the RS-485 interface checks if the request packet sent by the master device 101 is addressed to it.
For example, when the slave device 104 determines that the request packet has been addressed to it, the slave device 104 immediately sends a response packet to the master device 101, completing the polling process for a single slave device. At this point, only the slave device 104 can transmit data to the master device 101.
In such a polling scheme, even when a slave device wants to send data to the master device, the salve device cannot transmit data without permission of the master device. In addition, the request packet and the response packet have to be sent and received before every data transmission. As a result, in electronic devices employing such a polling scheme, communications may be slow and prone to delay. Such low communications speed and communications delay may become more serious as the number of electronic devices connected to the transmission line increases.